The present invention relates to a method for the fractionation of molasses using a chromatographic simulated moving bed system comprising at least two chromatographic partial packing material beds.
Fractionation of molasses denotes fractionation of various vegetable-derived by-products of the food and fermenting industries, such as beet and cane molasses, stillage, vinasse, slop, wood molasses, corn steep water, wheat, barley and corn molasses (hydrolyzed C starch).
The simulated moving bed system (SMB) has been developed and introduced by UOP (United Oil Products), U.S.A., at, the beginning of the 1960""s, initially for petrochemical applications (U.S. Pat. No. 2,985,589). Today several simulated moving bed methods for a number of different applications are known (U.S. Pat. Nos. 3,706,812, 4,157,267, 4,267,054, 4,293,346, 4,312,678, 4,313,015, 4,332,623, 4,359,430, 4,379,751, 4,402,832, 4,412,866, 4,461,649, 4,533,398 and 5,127,957, and published European application 0,279,946).
The simulated moving bed system enables separating performances that are many times higher, and dilution of the products (consumption of eluent) is lower than in the batch method.
The simulated moving bed method can be either continuous or sequential.
In a continuous simulated moving bed method, all flows are continuous. These flows are: feeding of feed solution and eluent liquid, recycling of liquid mixture and recovery of products (usually only two). The flow rate for these flows may be adjusted in accordance with the separation goals (yield, purity, capacity). Normally, 8 to 20 partial packing material beds are combined into a single loop. In accordance with the above-mentioned U.S. Pat. No. 4,402,832, the recycling phases have been applied to the recycling of e.g. non separated fraction and dilute fractions. The feed and product recovery points are shifted cyclically in the downstream direction. On account of the feed of eluent liquid and feed solution (and on account of recovery of products) and the flow through the packing material bed, a dry solids profile is formed. Ingredients having a lower migration rate in the packing bed are concentrated at the downstream end (back slope) of the dry solids profile, and respectively ingredients having a higher migration rate at the upstream end (front slope). Feeding points for feeding solution and eluent liquid and recovery points for product or products are shifted gradually at substantially the same rate at which the dry solids profile moves in the bed. The product or products are recovered substantially from the upstream and downstream end of the dry solids profile, and the feed solution is fed approximately to the maximum point of the dry solids profile and the eluent liquid approximately to the minimum point of the dry solids profile. Part of the separated product fraction is recycled on account of the continuous cyclic flow and as only part of the dry solids profile is removed from the packing material bed.
The cyclical shifting of the feed and recovery points can be performed by using feed and recovery valves disposed along the packing material bed at the upstream and downstream end of each partial packing material bed. If it is desired to recover product fractions of high purity, short phase times and a plurality of partial packing material beds must be employed (the apparatus has corresponding valves and feed and recovery equipment).
In a sequential simulated moving bed method, not all flows are continuous. In a sequential simulated moving bed method the flows can be: feeding of feed solution and eluent liquid, recycling of liquid mixture and recovery of products (two to four or more products; e.g. betaine as a third fraction in beet molasses separation and monosaccharides in cane molasses separation and lignosulphonates in spent liquor separation). The flow rate and the volumes of the different feeds and product fractions may be adjusted in accordance with the separation goals (yield, purity, capacity). The method comprises three basic phases: feeding, elution, and recycling. During the feed phase, a feed solution and possibly also an eluent liquid can be fed into predetermined partial packing material beds, and simultaneously two or even three product fractions can be recovered. During the eluting phase, eluent liquid can be fed into a predetermined partial packing material bed, and during said phases one or even two product fractions can be recovered in addition to the residue. During the recycling phase, no feed solution or eluent liquid can be fed into the partial packing material beds and no products can be recovered. The use of said phases is possible simultaneously in same or different beds.
Finnish Patent Application 882740 (U.S. Pat. No. 5,127,957) discloses a method for recovery of betaine and sucrose from beet molasses using a sequential simulated moving bed method, the chromatographic system therein comprising at least three chromatographic partial packing material beds connected in series, in which method betaine and sucrose can be separated during the same sequence comprising: a molasses feeding phase, in which a molasses feed solution can be fed into one of said partial packing material beds and in which eluent water can be fed substantially simultaneously into another partial packing material bed, a feeding phase of eluent water, and a recycling phase, these phases being repeated either once or several times during the sequence.
U.S. Pat. No. 4,631,129 discloses the separation of sugars and lignosulphonates from a sulphite spent liquor by a process comprising two chromatographic treatments with ion exchange resins in different ionic forms. In the first treatment, the sulphite spent liquor is introduced into a chromatographic column comprising a strong acid cation exchange resin used as column packing material in metal salt form; the metal ion is preferably a metal ion of the spent liquor, usually calcium or sodium. A substantially sugarless fraction rich in lignosulphonates and a fraction rich in sugars are obtained from this column by elution. The latter fraction is subjected to a softening treatment, and its pH is adjusted to be in the range 5.5 to 6.5, whereafter it is introduced into the second chromatographic column containing resin in monovalent form, and a second fraction rich in sugars and a second fraction rich in lignosulphonates and salts are obtained therefrom by elution. It is stated in this patent that the process is capable of recovering sugars, e.g. xylose contained in hardwood sulphite spent liquor, in a very high purity and high yields. However, a drawback of the method of U.S. Pat. No. 4,631,129 is that the dry solids profile, which has been formed in the first chromatographic treatment and in which the components are already partly separated can be destroyed in the softening treatment and pH adjustment and thus may not be effectively utilized in the second chromatographic treatment. The method of U.S. Pat. No. 4,631,129 can be also complicated by the steps of concentration and additional pumping to which the solution is subjected. All of these factors add to investment costs. Furthermore, the method of U.S. Pat. No. 4,631,129 and many prior art chromatographic separation methods are attended by the drawback that they are typically batch methods and are not suitable for fractionating solutions on an industrial scale.
U.S. Pat. Nos. 4,008,285 and 4,075,406 teach recovery of xylose by a chromatographic method. In this method, a pentosan-containing biomass, e.g. wood raw material, is hydrolysed, the hydrolysate is purified by ion exclusion and colour removal and the resultant solution is fractionated chromatographically to obtain a solution rich in xylose. The fractionating methods disclosed in these patents are also batch processes, and only two product fractions are disclosed to be obtained thereby.
It is known that sucrose and betaine are recoverable from molasses by chromatographic separation. U.S. Pat. No. 4,395,430 describes a chromatographic method for the recovery of betaine from molasses by a batch process in which diluted molasses is fractionated with a polystyrene sulphonate exchange cation exchange resin in alkali metal form. In the method of U.S. Pat. No. 4,395,430 the betaine-enriched fraction obtained from a first fractionation is subjected to further chromatographic purification. However, the dry solids content in the sucrose and betaine fractions obtained by this method is relatively low and therefore, large amounts of eluent water usually need to be evaporated when recovering the sucrose and betaine from their respective fraction by crystallization.
U.S. Pat. No. 5,730,877 describes a method for fractionating a solution, such as sulphite cooking liquor, molasses, vinasse, etc., by a chromatographic simulated moving bed (SMB) method in which the liquid flow is effected in a system comprising at least two sectional beds in different ionic form. The liquid present in sectional packing material beds with its dry solids (dry substance) separation profile is recycled during the recycling phase in a loop. The dry solids separation profile from the first process phase can be retained and fed into the second process phase. This can have considerable benefit over many conventional two step processes where the dry solids separation profile is normally mixed in tanks between the columns.
German Patent DE 1 692 889 discloses recovery of xylose from sulphite spent liquor by a method in which the spent liquor is extracted with aliphatic alcohols containing 1 to 5 carbon atoms, the water and alcohol layers formed are separated, alcohol is removed from the latter by distillation, and the resultant syrup-like residue in which the ratio of xylose to lignosulphonates is at most 1:2.5, is maintained at a temperature below room temperature until the xylose is crystallized. The crystallized xylose is ground with ethanol, filtered, and dried. In this method, the lignosulphonates remain in the mother liquor with the salts. The drawback of the process is the recovery of solvents.
It is, therefore, desirable to provide an improved method to recover products from molasses.
An improved method is provided to process molasses, such as: beet molasses, cane molasses, stillage, vinasse, wood molasses, biomass molasses, wheat molasses, barley molasses, corn molasses, and solutions derived from any of the preceding. The solutions derived from the molasses can comprise: raw juice, diffusion juice, thick juice, dilute juice, residual juice, molasses-containing liquid, or another molasses-containing juice. Advantageously, the improved method can produce a purer and/or better yield product.
The wood molasses and the biomass molasses can be derived from a xylan-containing vegetable material, such as: wood, hardwood as, birch, aspen, beech, eucalyptus, poplar, alder and alm, particulates of grain as straw, stems, hulls, husks, fibers, grains as wheat, corn, barley, rice, oat, corn cobs, bagasse, almond shells, coconut shells, cotton seed bran, cotton seed hulls, rice hulls, wood chips, and/or saw dust.
The biomass molasses can also comprise biomass hydrolysates. The biomass hydrolysates can be obtained by a process, such as: direct acid hydrolysis of biomass prehydrolysate obtained by prehydrolysis of biomass with steam or by enzymes, steam explosion of biomass, acid hydrolysis of prehydrolysate obtained by prehydrolysis of biomass with acetic acid, steam or enzymes, or spent liquor from pulping process such as a sulphite pulping process.
The wood molasses and the biomass hydrolysates can comprise: sulphite cooking liquor, spent sulphite pulping liquor, acid spent sulphite liquor, spent liquor from hardwood pulping, spent liquor from softwood pulping before or after hexoses are partially removed, spent liquor after ultrafiltration, spent liquor from digestion of biomass, spent liquor from hydrolysis of the biomass, spent liquor from solvent-based pulping, spent liquor from ethanol-based pulping, mother liquor from crystallization of xylose, diluted runoff of xylose crystallization from sulphite spent pulping liquor based solution, waste solution(s) from the paper industry, and/or from the pulping industry.
In one preferred method of this invention, at least one product is recovered during processing of molasses in two or more loops, i.e. at least a first loop and a second loop. Each loop comprises one or more chromatographic beds, columns, or parts thereof which are separate and distinct from the chromatographic beds, columns, and parts thereof in the other loop(s). The loops can be open or closed. A solution, liquid, or fraction from one loop can be transferred or passed to another loop when the loops are open. The system of the preferred method can comprises one to twelve chromatographic columns. Each loop can comprise a series of columns containing as a column filling material a cation exchange resin. Preferably, a strongly acid cation exchange resin comprises the beds. The strongly acid cation exchange resin can be in monovalent or divalent form. The monovalent form can comprise e.g. sodium, potassium or mixtures thereof. The divalent form can comprise e.g. calcium and magnesium or mixtures thereof.
Processing can occur in at least one of the following phases: a feeding phase, an eluting phase, or a recycling or circulation phase, and a product recovery phase. Desirably, liquid present in each loop comprises one or more separate dry solids profiles (dry solids profiles) and the dry solids profiles is recycled in the recycling phase of the loop. The dry solids profile(s) is also advanced during other phases such as the feeding phase, the eluting phase, and the product recovery phase. In one of the methods, a recycled fraction is recovered from the second loop and recycled to the first loop. The feed solution can also be derived from or contain part or all of the recycle fraction. Each loop is preferably different than the other loop and the dry solids profile(s) (dry substance profiles) can be recycled in all phases. Columns in the loops can be in the same phase or a different phase with each other. Advantageously, at least some of the phases during the processing of the molasses occur sequentially, continuously, or simultaneously.
Each loop can comprise a series of columns containing a cation exchange resin. The simulated moving bed (SMB) process in the first loop can be a continuous simulated moving bed (SMB) process or a sequential moving bed (SMB) process. The chromatographic fractionation in the second loop can comprises a batch method. Preferably, the chromatographic fractionation in the second loop comprises a continuous simulated moving bed (SMB) process or a sequential simulated moving bed (SMB) process. In one preferred embodiment the first loop is a continuous SMB and the second loop is a sequential SMB.
As used in this application, the term xe2x80x9cdry substance profilexe2x80x9d or xe2x80x9cdry solids profilexe2x80x9d can be considered to be the dry substance concentration profile in the chromatographic separation resin beds, which is formed during the operation of a simulated moving bed (SMB) process by feeding the feed solution and eluent into one or more separation columns in the loops and collecting the product fractions from one or more loops. Fast moving components are concentrated in the front slope of the dry substance profile and slowing moving components are concentrated in the back slope of the dry substance profile.
By feeding eluant and feed solution containing constituents, by withdrawing product fractions, and by the flow through the chromatographic bed(s), a dry solids profile is formed in the chromatographic bed(s) constituents having a relatively low migration rate in the chromatographic bed are concentrated in the back slope of the dry solids profile, while constituents having a higher migration rate are concentrated in the front slope of the dry solids profile.
The liquid(s) present in the partial packing material beds with their dry solids profile(s) can be recycled in the recycling phase in a loop comprising one, two or several partial packing material beds. xe2x80x9cPartial packing material bedxe2x80x9d as used in this application can mean a section of a chromatographic separation resin bed, which is separated from the other sections of one or more resin beds, by some means, such as by intermediate bottoms, feeding and collection devices or partial packing material beds which are located in the separate columns.
In sequential or continuous simulated moving bed (SMB) systems, the chromatographic bed(s) is typically divided into sub-sections. A chromatographic beds is usually packed with some type of chromatographic adsorbent, packing material. xe2x80x9cPartial packing material bedxe2x80x9d can be any kind of sub-section of the chromatographic bed. The chromatographic bed(s) can be constructed of a single column or multiple columns, which are divided into section or compartments. The chromatographic bed can also be constructed of several discrete columns, tanks, or vessels, which are connected by pipelines.
Processing in the first loop can comprises one or more of the following phases: one or more molasses feeding phases, one or more feeding phases of an eluent liquid, one or more recycling phases, and/or one or more recovery phases of at least one product. Processing in the second loop can include one or more feeding phases, one or more recycling phases, one or more feed phase of eluent liquid and/or product recovery phase. The processing can comprise a plurality of recycling phases. The processing can also comprise five to ten steps or twenty steps, which form a sequence which is repeated. In one preferred method, the sequence is repeated five to seven times in order to reach an equilibrium in the system, and the method is continued essentially in the state of equilibrium. A sequence can comprise steps during which different beds are in the same or different phases simultaneously
Processing of the molasses can further comprise feeding a feed solution derived from the molasses in the first loop and, subsequently, fractionating the feed solution in the first loop by a chromatographic simulated moving bed (SMB) process into at least two fractions, preferably at least one product fraction and at least one residual fraction. At least one of the fractions from the first loop, preferably a product fraction from the first loop, can be crystallized to form a crystallized fraction. A liquid, such as a solution or mother liquor, derived from the crystallization run-off of the crystallization of a fraction from the first loop, e.g. a product fraction from the first loop, can then be fed to the second loop where it is fractionated by chromatographic fractionation into at least two other fractions, preferably at least one other product fraction and at least one other residual fraction.
In the method, at least one of the fractions comprises a product fraction such that the product fraction comprises a greater percentage concentration by weight on a dry solids basis (dry substance basis) of the product than the feed solution comprising the molasses. Preferably, the product fraction also comprises a greater percentage concentration by weight on a dry solids basis of the product than the solution derived from the crystallization run-off. In the preferred method, (1) the product fraction from the first loop comprises a greater percentage concentration by weight on a dry solids basis of the product than the feed solution comprising the molasses and (2) the product fraction from the second loop comprises a greater percentage concentration by weight on a dry solids basis of the product than the feed solution comprising the molasses. In one preferred method, the product fraction from the second loop also comprises a greater concentration by weight on a dry solids basis of the product than the solution derived from the crystallization run-off from the crystallization after the first loop.
The fractions obtained from the fractionation in the first loop and/or the second loop can comprise one or more: sucrose fractions, betaine fractions, xylose fractions, residual fractions, or recycled fractions. Furthermore, the preceding fractions can comprise one or more compounds comprising: sucrose, betaine, xylose, glucose, galactose, rhamnose, mannose, and/or xylonic acid. The feed solution can comprises one or more compounds of: betaine, carbohydrates, sugars, sugar alcohols, ionic substances, divalent ions, monosaccharides, hexoses as glucose, galactose, mannose and rhamnose pentoses as xylose and arabinose, lignosulphonates, oligosacchadries and combinations of the preceding.
The product fraction(s) can be recovered from the first loop and/or the second loop. In one preferred method, the product fraction comprises a sucrose fraction. One of the fractions from the first loop and/or the second loop can comprise a betaine fraction. Preferably, the betaine fraction, comprises a greater percentage concentration of betaine by weight on a dry solids basis than at least one of the other fractions in the loops.
In another preferred method, the product fraction comprises a xylose fraction. The molasses can also comprise a xylose solution.
The feed solution can be pretreated before being fed to the first loop in at least one pretreatment process, such as: filtering, ultrafiltration, heating, chromatography, concentrating, evaporation, neutralization, pH adjustment, dilution, softening by carbonation, ion exchange or combinations of the preceding. Furthermore, the solution derived from the crystallization run-off, which is fed and fractionated in loop 2, can be treated before being feed and fractionated into loop 2, in at least one treatment process such as: filtering, ultrafiltration, heating, concentrating, evaporation, neutralization, pH adjustment, dilution, softening by carbonation, ion exchange or combinations of the preceding. Xylose can be converted into xylitol e.g. by hydrogenation before the loops between the loops or after the loops.
In the preferred method, the product fractions comprise sucrose fractions or xylose fractions. The product fraction(s) can be crystallized into a crystallized product, such as sugar, xylose or xylitol. Xylitol can be crystallized by e.g. cooling crystallization.
The invention offers an advantageous method particularly for the recovery of xylose from hardwood sulphite cooking liquor. The sulphite cooking liquor can be the liquor used in the cooking of sulphite cellulose, or the liquor ensuing from its cooking, or a part thereof. In one embodiment of the method, lignosulphonates can be recovered as the most rapidly eluted fraction and xylose which is the slowest to elute can be recovered as the product fraction.
The sulphite cooking liquor can comprise cooking chemicals, undissolved wood material, lignosulphonates, organic acids, hexose and pentose sugars derived as hydrolysis products of hemicellulose, as well as small amounts of oligosaccharides, if hydrolysis into monosaccharides has been incomplete. Normally a low pH in pulp cooking contributes to the hydrolysis of hemicellulose into monosaccharides. When the pulp is produced from hardwood, the major part of the monosaccharides contained in the cooking liquor can consist of xylose, which can be employed as a raw material in the production of crystalline xylose, xylitol and/or furfural. When pulp is produced from softwood, the prevalent monosaccharide in the cooking liquor is mannose.
A more detailed explanation of the invention is provided in the following description and appended claims taken in conjunction with the accompanying drawings.